1. Field of the Invention
The present invention relates to optical apparatuses, such as video lenses, video cameras, TV lenses or TV cameras, equipped with an auto-focusing (AF) function.
2. Description of Related Art
Optical apparatuses equipped with an AF function are known in which a signal corresponding to the sharpness (contrast state) of an object image is extracted from an image-pickup signal (video image) and evaluated to perform a focus adjustment operation with an image-taking optical system.
FIG. 33 is a block diagram showing the structure of a conventional optical apparatus. In this figure, reference numeral 201 denotes the optical apparatus, reference numeral 202 denotes a focus lens constituting an image-taking optical system, reference numeral 203 denotes a CCD (image-pickup device) which converts input optical signals into electrical signals and outputs them as video signals, reference numeral 204 denotes a video signal processing section which processes video signals output from the CCD 203, reference numeral 205 denotes an AF evaluation section which generates an AF evaluation value signal representing a sharpness, based on the processed video signal, reference numeral 206 denotes a CPU which controls a motor 207 driving the focus lens 202 based on the AF evaluation value signal from the AF evaluation section 205. Numeral 208 denotes a lens position detection section which detects the position of the focus lens 202 and inputs the current position of the focus lens 202 as a feedback signal to the CPU 206.
The light passing through the focus lens 202 forms an image on an image-pickup surface of the CCD 203, and is converted by the CCD 203 into video signals. The video signal processing section 204 processes the video signal from the CCD 203 with a filter or the like, and optimizes the video signal. The AF evaluation section 205 generates an AF evaluation value signal representing the sharpness of the object image from the video signal obtained within a focus detection area which is set at a center of an image-taking area.
Here, since the focus detection area is set to the center of the image-taking area, the image-taking optical system is focused on the object positioned at the center of the image-taking area. Being mechanically connected to the focus lens 202, the lens position detection section 208 detects the position of the focus lens 202, and inputs a position feedback signal into the CPU 206. Based on the AF evaluation value signal from the AF evaluation section 205 and the position feedback signal obtained from the lens position detection section 208, the CPU 206 calculates the driving quantity of the focus lens 202, and inputs a driving command signal into the motor 207. The motor 207 is operated with this driving command signal, and drives the focus lens 202. Thus, a focusing process towards the object is carried out.
However, in this conventional example, the position of the focus detection area is fixed to the central area of the image-taking area, and also the size of the focus detection area is fixed. Therefore, if the size of the object in the image-taking is not of a suitable size compared to this fixed focus detection area, or if it is necessary to perform image-taking such that the object is positioned outside the central area in the image-taking area, then it is not possible to perform an adequate focusing process.